The present invention relates to a method and apparatus for cooling the inner surface of metal pipes.
In a known method of continuously hardening a metal pipe which comprises the steps of heating the metal pipe as it passes through a heating unit and then cooling the inner surface of the metal pipe, as shown in FIGS. 1(a) and 1(b), the cooling of the inner surface of a metal pipe 1 is accomplished by placing an annular cooling nozzle 2 within the metal pipe 1. A heating unit 3 for hardening puposes is arranged on the outer side of the metal pipe. A plurality of nozzle openings 4 are formed in the outer periphery of the annular nozzle 2 so that cooling water 6 supplied through a water supply duct 5 may be sprayed against the pipe inner surface. A disadvantage of this arrangement is that the water pressure at each of various points on the nozzle circumference differs from one another with the resulting difference in the rate of water flow from the nozzle openings 4 and moreover there are other detrimental factors such as retention of water on the pipe inner surface and the presence of water streams flowing opposite to the direction of travel of the pipe, thus giving rise to non-uniform cooling of the pipe, thereby causing non-uniform hardening of the pipe.
Although various methods including the method of quenching a metal pipe while rotating the pipe as it passes through the unit and the method of quenching a metal pipe by a rotating cooling nozzle have been proposed to overcome the foregoing deficiencies, when large diameter pipes are to be treated all of these conventional methods require a complicate equipment and thus satisfactory maintenance of such equipment is difficult.